[Feature request] add `each` mode to batch edit PRs in a stack

If I want to request the review of each PR to a list of collaborators, I need to loop `gh stack up && gh pr edit --add-reviewer ...` for each PR in the stack, while with:
```sh
$ gh stack each edit --add-reviewer ....
```
the `edit --add-reviewer` command could be applied to each PR of the stack automatically with a single request.

If we would like to limit the `each` scope only to the `pr edit` action, then we could simplify it as:
```sh
$ gh stack each --add-reviewer ....
```

首先跟踪现有的 `gh stack up` 和 `gh pr edit` 入口，以及如何获取 stack 的 PR 列表。比较提出的两种命令形式，然后将完成定义为通过一次调用将请求的编辑应用于 stack 中的每个 PR，同时包括对所选接口的覆盖。

由索引模型根据 Issue 内容生成。